Re: [Qemu-devel] [PATCH v2 23/54] qapi-commands: add #if conditions to commands

[Marc-André Lureau]

----- Original Message -----
> Hi
> 
> ----- Original Message -----
> > Marc-André Lureau <address@hidden> writes:
> > 
> > > Wrap generated code with #if/#endif using the ifcond_decorator.
> > >
> > > Signed-off-by: Marc-André Lureau <address@hidden>
> > > ---
> > >  scripts/qapi-commands.py  | 2 ++
> > >  tests/test-qmp-commands.c | 4 ++--
> > >  2 files changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
> > > index 5eb96b2d95..db45415c41 100644
> > > --- a/scripts/qapi-commands.py
> > > +++ b/scripts/qapi-commands.py
> > > @@ -228,6 +228,7 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> > >          self.defn = None
> > >          self._regy = None
> > >          self._visited_ret_types = None
> > > +        self.if_members = ['decl', 'defn', '_regy']
> > >  
> > >      def visit_begin(self, schema):
> > >          self.decl = ''
> > > @@ -240,6 +241,7 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> > >          self._regy = None
> > >          self._visited_ret_types = None
> > >  
> > > +    @ifcond_decorator
> > >      def visit_command(self, name, info, arg_type, ret_type,
> > >                        gen, success_response, boxed, ifcond):
> > >          if not gen:
> > > diff --git a/tests/test-qmp-commands.c b/tests/test-qmp-commands.c
> > > index 9b9a7ffee7..ad7b6e4e1d 100644
> > > --- a/tests/test-qmp-commands.c
> > > +++ b/tests/test-qmp-commands.c
> > > @@ -10,11 +10,11 @@
> > >  
> > >  static QmpCommandList qmp_commands;
> > >  
> > > -/* #if defined(TEST_IF_CMD) */
> > > +#if defined(TEST_IF_CMD)
> > >  void qmp_TestIfCmd(TestIfStruct *foo, Error **errp)
> > >  {
> > >  }
> > > -/* #endif */
> > > +#endif
> > >  
> > >  void qmp_user_def_cmd(Error **errp)
> > >  {
> > 
> > To find out whether the clever decorator is worth its keep, I replaced
> > it with the dumbest, most obvious code I could think of (appended).
> > Does this make visit_command() easier or harder to understand?
> > 
> > 
> > 
> > diff --git a/scripts/qapi-commands.py b/scripts/qapi-commands.py
> > index db45415c41..13d37d2ac2 100644
> > --- a/scripts/qapi-commands.py
> > +++ b/scripts/qapi-commands.py
> > @@ -228,7 +228,6 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> >          self.defn = None
> >          self._regy = None
> >          self._visited_ret_types = None
> > -        self.if_members = ['decl', 'defn', '_regy']
> >  
> >      def visit_begin(self, schema):
> >          self.decl = ''
> > @@ -241,18 +240,21 @@ class QAPISchemaGenCommandVisitor(QAPISchemaVisitor):
> >          self._regy = None
> >          self._visited_ret_types = None
> >  
> > -    @ifcond_decorator
> >      def visit_command(self, name, info, arg_type, ret_type,
> >                        gen, success_response, boxed, ifcond):
> >          if not gen:
> >              return
> > -        self.decl += gen_command_decl(name, arg_type, boxed, ret_type)
> > +        decl = gen_command_decl(name, arg_type, boxed, ret_type)
> > +        defn = ''
> >          if ret_type and ret_type not in self._visited_ret_types:
> >              self._visited_ret_types.add(ret_type)
> > -            self.defn += gen_marshal_output(ret_type)
> > -        self.decl += gen_marshal_decl(name)
> > -        self.defn += gen_marshal(name, arg_type, boxed, ret_type)
> > -        self._regy += gen_register_command(name, success_response)
> > +            defn += gen_marshal_output(ret_type)
> > +        decl += gen_marshal_decl(name)
> > +        defn += gen_marshal(name, arg_type, boxed, ret_type)
> > +        self.decl += gen_ifcond(ifcond, decl)
> > +        self.defn += gen_ifcond(ifcond, defn)
> > +        self._regy += gen_ifcond(ifcond,
> > +                                 gen_register_command(name,
> > success_response))
> 
> This is one of the most simple case, and it is already very intrusive. If you
> have more branches / early return it becomes awful.
> 
> Do it for all the places where we have @ifcond_decorator and you will
> probably prefer the concise decorated version. For me this case is one of
> the reason why decorators exist: to wrap enter/exit of a function.
> 

Oh and your version looks inferior, since it will generate empty #if/#endif 
blocks. You seemed to be quite strict about having the generated output be 
nicely formatted & human friendly, so I thought clearing those empty block was 
a must for you.

> >  
> >  
> >  (input_file, output_dir, do_c, do_h, prefix, opts) = parse_command_line()
> > diff --git a/scripts/qapi.py b/scripts/qapi.py
> > index 52099332f1..3de5b8b8f0 100644
> > --- a/scripts/qapi.py
> > +++ b/scripts/qapi.py
> > @@ -1918,29 +1918,10 @@ def gen_endif(ifcond):
> >      return ret
> >  
> >  
> > -# Wrap a method to add #if / #endif to generated code, only if some
> > -# code was generated.
> > -# self must have 'if_members' listing the attributes to wrap.
> > -# The last argument of the wrapped function must be the 'ifcond'.
> > -def ifcond_decorator(func):
> > -
> > -    def func_wrapper(self, *args, **kwargs):
> > -        ifcond = args[-1]
> > -        save = {}
> > -        for mem in self.if_members:
> > -            save[mem] = getattr(self, mem)
> > -        func(self, *args, **kwargs)
> > -        for mem, val in save.items():
> > -            newval = getattr(self, mem)
> > -            if newval != val:
> > -                assert newval.startswith(val)
> > -                newval = newval[len(val):]
> > -                val += gen_if(ifcond)
> > -                val += newval
> > -                val += gen_endif(ifcond)
> > -            setattr(self, mem, val)
> > -
> > -    return func_wrapper
> > +def gen_ifcond(ifcond, ctext):
> > +    if ifcond:
> > +        return gen_if(ifcond) + ctext + gen_endif(ifcond)
> > +    return ctext
> >  
> >  
> >  def gen_enum_lookup(name, values, prefix=None):
> > 
>